a. Field of the Invention
This invention relates to methods for bonding moisture-containing nonwoven webs made from polyamide filaments.
B. Description of the Prior Art
Various methods of bonding nonwoven webs are known. For example, U.S. Pat. No. 3,647,591 discloses a process for bonding a web made up of a blend on nylon fibers and fibers of another kind which are not affected by a strong acid such as hydrochloric acid. The acid is applied to the web from an aqueous solution by spraying or dipping, with the fabric then being hot calendered to bond the nylon filaments in the web together. Under these conditions, the acid dissolves the nylon filaments so that these filaments more or less serve as an adhesive which bonds the entire web together, the other filaments in the web providing strength.
U.S. Pat. No. 3,647,244 discloses a process for bonding a web made from polyamide filaments wherein the web is passed through a preconditioning zone such that the web picks up from 3 to 6 weight percent of water, with the web then being passed through a second zone where the web absorbs a hydrogen halide gas and additional moisture. The purpose of the preconditioning step is to allow the web to pick up the gas at a higher rate. The web is then pressed and self-bonded by washing it in water at room temperature to remove the absorbed gas.
It is known to autogenously bond a web made from polyamide filaments by applying a mixture of an activating agent and water in vapor form to the web and then passing the web between rolls at room temperature. One disadvantage of this process is that ambient humidity has an effect on the amount of bonding achieved when the web is passed between the rolls. It is well known that nylon filaments readily absorb moisture. Under conditions of high ambient relative humidity the web will contain more moisture when it passes between the rolls than at conditions of low ambient relative humidity. The result is bonding which is not uniformly consistent.